as.data.table.ffdf: S3 methods to convert between FFDF and data.table

In CALIBERdatamanage: Data Management Tools for CALIBER Datasets

Description

Converts a Flat File Data Frame (ffdf) to a data.table object, or the other way around. FFDF is a convenient form for storing very large datasets without using RAM, but data.table is faster and convenient for data processing.

Also converts cohort objects from data.table cohorts to ffdf cohorts and vice versa.

Usage

## S3 method for class 'ffdf'
as.data.table(x, keep.rownames = FALSE, ...)
## S3 method for class 'cohort'
as.data.table(x, keep.rownames = FALSE, ...)
## S3 method for class 'data.table'
as.ffdf(x, vmode = NULL,
    col_args = list(), ...)
## S3 method for class 'cohort'
as.ffdf(x, vmode = NULL,
    col_args = list(), ...)

Arguments

x	object to convert (FFDF data frame, data.table or cohort). FFDF objects must have more than one row in order to be converted to data.table.
keep.rownames	TRUE will retain the rownames of x in a column named rn.
vmode	optional specification of the vmodes of columns of the data.frame. Either a character vector of vmodes (named with column names of the data.frame or recycled if not named) or a list named with vmodes where each element identifies those columns of the data.frame that should get the vmode encoded in the name of the element
col_args	further arguments; passed to ff
...	further arguments: passed to ffdf for .ff_vector, .ff_matrix and .data.frame methods; passed to as.data.table for as.data.table methods; ignored for .ffdf identity method

Details

If these functions are provided in the ffdf or data.table packages, they will be removed from this package. as.ffdf.data.table is a convenience function which automatically converts characters to factors in the original data.table then calls as.ffdf.data.frame.

Value

as.ffdf returns a FFDF object; as.data.table returns a data.table object. If the original object is a cohort, the output is also a cohort.

Author(s)

Anoop Shah

See Also

importDT, importFFDF

Examples

mydatatable <- data.table(a = 1:6, b = 'this')
mydatatable

# Convert to ffdf (column b will be converted to a factor)
myffdf <- as.ffdf(mydatatable)
myffdf

# Convert back to data.table (column b remains as a factor)
as.data.table(myffdf)
str(mydatatable)

CALIBERdatamanage documentation built on Nov. 23, 2021, 3 p.m.